This invention relates to an apparatus for loading a predetermined amount of columnar materials such as nuclear fuel pellets into a fuel rod cladding tube.
Generally, with the nuclear fuel rod used in a nuclear reactor, and particularly, with the fuel rod used in a boiling water reactor (BWR), a space in the fuel rod is divided axially into a plurality of areas or sections, and with respect to these sections, the nuclear fuel pellets containing U.sub.235 of different enrichment, respectively, are loaded into fuel cladding tubes for the purposes of axially even distribution of the power output in BWR, shut-down margin of the reactor, an economical point of the fuel, and the like. For these purposes, in the prior art technique, there is proposed a fuel cladding tube having a plurality of sections into which the pellets having poison materials with densities different from each other are loaded. With a fuel rod in a pressurized water reactor (PWR), there is not observed unevenness in the axial direction of the power output in PWR dependent to void such as in the BWR, but a consideration will have to be paid on the economical point of the nuclear fuel. In addition, with a fast breeder reactor (FBR), the pellets have to be loaded into sections of a blanket portion and a fuel portion arranged in the axial direction of the cladding tube.
Moreover, in addition to the fact that a plurality of sections are located in one fuel rod, a length of a row of pellets to be loaded is generally different with respect to the types of the reactors, for example, only in case of the BWR.
In this connection, on the view point of a fuel fabrication process, in a case where the fuel rod only for the BWR is fabricated, the whole length of a row of the pellets to be loaded is different with respect to the respective types of the nuclear reactor, the designs of the respective section of the cladding tube in the axial direction are also different with respect to the types of the fuel rods to be used, and the kinds of the pellets to be loaded are also different with respect to the respective sections. In spite of the above facts, it is required to correctly load the pellets having substantially the same shapes respectively for the fuel rods of various types, and accordingly, a relatively long time is required for the fabrication of the nuclear fuel, which further results in the cost-up for the fuel fabrication, thus being not economical.
FIG. 1 shows a longitudinal section of a nuclear fuel rod of general type, in which a predetermined number of pellets 2 each essentially consisting of an uranium dioxide are loaded in a cladding tube 1 made of, for example, zirconium alloy or stainless steel and the pellets 2 are pressed at one end by spring means 3 towards the other end. At both the ends of the cladding tube 2 are welded end plugs 4 and 5, respectively. Accordingly, as shown in FIG. 2, two sections, i.e. section A, having a longitudinal length L.sub.1, in which the pellets 2 are loaded and plenum section B, having a longitudinal length L.sub.2, in which no pellet is loaded, are formed in the cladding tube 1 of the nuclear fuel rod. The plenum section B is designed to have a longitudinal length sufficient for storing or retaining a generated fission gas and the longitudinal length of the section A is determined in accordance with the length of the section B.
In order to arrange the fuel pellets axially in a row in the cladding tube so as to have a predetermined length, are generally known a method in which longitudinal lengths of the pellets are respectively measured and added or a method in which the pellets are manually aligned so as to have a length corresponding to a marking-off line which is preliminarily marked on a tray on which the pellets are disposed.
In the methods described above in which desired length of the pellets is measured, however, a length measuring working or operation is considerably troublesome, requires much time and may involve a relatively large cumulative error. Furthermore, in a case where the tray to which the marking-off line is applied is used, it will be required to prepare many kinds of trays in accordance with the kinds of the fuel rods and to selection necessary one of these trays as occasion demands. The necessity for manually adjusting or aligning the whole length of the respective lengths of the pellets also requires much time and labor.
In the other point of view, in which the pellet loading area A is divided into a plurality of sections in accordance with the kidns of pellets, the lengths of the respective section are generally prescribed in the manner described hereunder.
As shown in FIG. 3, for example, the area will be divided into five sections A.sub.1 through A.sub.5 having longitudinal lengths l.sub.1, (l.sub.2 -l.sub.1), (l.sub.3 -l.sub.2), (l.sub.4 -l.sub.3) and (L.sub.1 -l.sub.4), respectively, and the plenum section B has the length L.sub.2, or as shown in FIG. 4, the area will be divided into five section A.sub.1 through A.sub.5 having the longitudinal lengths l.sub.1, l.sub.2 ', l.sub.3 ', l.sub.4 ' and {L.sub.1 -(l.sub.1 +l.sub.2 '+l.sub.3 '+l.sub.4 ')}, respectively, and the plenum section has the length L.sub.2.
With both the methods described above, the tolerances in the lengths of the respective sections A.sub.1 through A.sub.4 and the area A are set to be slightly longer than the length of one pellet so that the length of the pellet row will be ranged within the tolerance on the basis of the fact as to whether or not further one pellet should be added into the pellet row to be loaded.
In a case where it is desired to load the pellets into four sections of the fuel rod by a conventional method as shown in FIG. 5, plural kinds of fuel pellets 2Ba, 2b, 2c and 2d are arranged in an aligned manner in transporting trays 6, respectively, which are disposed in a row on a loading table 7 in accordance with the pellet loading order. The table 7 is provided with a V-shaped groove as a tray 8 on one longitudinal side thereof and the tray 8 is sectioned by a plurality of dividing members a.sub.1, a.sub.2 a.sub.3, a.sub.4 and a.sub.5 designed in accordance with the fuel rod so that one row of pellets of the respective transporting trays 6 can be loaded in the corresponding sections of the tray 8 divided by the dividing members a.sub.1, a.sub.2, a.sub.3, a.sub.4 and a.sub.5, and thereafter, the pellet row in the tray 8 is loaded into the fuel cladding tube 1. The fact, however, that these operations must be done by manual working or hand operation requires confirmation of the operator as to whether or not the same kinds of pellets or trays are always arranged and loaded on the predetermined positions without failure in addition to the confirmations of the kinds and the lengths of the pellets in the respective sections. This fact requires much time and labour, thus being not effective, and the increasing of the loading speed without taking any specific care will result in miss-loading of the pellets.